The present invention relates to neon sign control devices which perform switching and brightness adjustment of discharge tubes for decorative illumination, such as a neon tube or an argon tube.
In order to light discharge tubes for decorative illumination such as a neon tube sign or an argon tube sign (hereinafter referred to as "neon sign"), a special transformer of magnetic leakage type (hereinafter referred to as "neon transformer") has been used. The primary side of a neon transformer is turned on and off using a mechanical contact system comprising a brush and a rotary drum; thereby an a.c. current is supplied and interrupted to the neon transformer so as to perform switching control of a neon tube connected to the secondary side of the neon transformer.
In such a switching system of the prior art, however, use of mechanical contacts may cause problems due to contact abrasion, contact failure or insulation failure. Contacts of working state are liable to abnormal heating resulting in a fire. Consequently, the system has problems not only in function but also in prevention of disasters, and much labor is required for maintenance control. The neon tubes and the neon transformers are usually mounted on a so-called advertising pillar installed on a roof of a building, and the switching control device is installed indoors remote from the advertising pillar. Consequently, wiring between the switching control device and the neon transformers must be performed inconveniently using thick wires over a long distance. As the scale of the neon advertising pillar becomes large, the wiring amount is significantly increased and therefore the manufacturing cost is increased.
Switching operation at the primary side of the neon transformer is accompanied by on/off operation of large current which generates electric noise to affect radio apparatuses adversely. This has caused a social problem.
In a relatively large advertising pillar, a plurality of neon transformers are used and neon tubes connected to the neon transformers are controlled in various flashing modes, for example. In order to obtain the intended flashing mode in the prior art, the lengths of contact segments on a rotary drum for the respective neon transformers, and their positions in the circumferential direction are selected. However, the device becomes large in such an arrangement and has many disadvantages as above described. Furthermore, in order to vary the flashing mode, the rotary drum must be exchanged and this is troublesome and involves high cost.
In general, neon signs for advertisement, irrespective of their scale, are lit when it becomes dark in the evening and put out after a definite time (at night) in consideration of economy. If the scale of the advertising neon signs is large, the turning on and off of a power switch are performed automatically. If it is small, control of turning on and off of a power switch is usually performed in manual operation. This is because the automatic control requires a relay, a timer and the like separately and therefore the device becomes expensive and the construction cost causes a serious problem in expense. Use of a timer of the motor type or spring type and the mechanical contacts makes the life relatively short. Since the control device must be installed at a site which is prevented from wetting by rain and free from moisture, i.e. indoors, it is inevitably installed remote from the neon transformer and therefore the construction cost becomes high also from this aspect. When control is effected in manual operation, not only labor is required but also forgetting of the turning on/off of the power switch may occur. Consequently, the manual operation is not always performed economically.